1. RNA and Protein
Synthesis
Section 12–3
This section describes RNA and its role
in transcription and translation.

2. The Structure of RNA
List the three main differences between RNA
and DNA.
1. RNA has ribose sugar instead of deoxyribose.
2. RNA is generally single-stranded, instead of
double-stranded.
3.RNA contains uracil in place of thymine.

3. Purpose of RNA
Is the following sentence true or false?
► RNA is like a disposable copy of a DNA
segment.
► True

4. What is the importance of the cell’s ability to
copy a single DNA sequence into RNA?
► It makes it possible for a single gene to
produce large numbers of RNA molecules.

5. Types of RNA
What is the one job in which most RNA
molecules are involved?
► Most are involved in
protein synthesis.

6. Types of RNA
► Complete the compare-and-contrast table
about the types of RNA.

7. Type Function
• Carries copies of the instructions for assembling amino
acids from DNA to the rest of the cell.
• Ribosomal RNA is a part of ribosomes.
• Transfer RNA Transfers each amino acid to the
ribosome to help assemble
proteins

8. Transcription
Circle the letter of each sentence that is true about
transcription.
• b. RNA polymerase uses one strand of DNA as a
template to assemble nucleotides into
a strand of RNA.
• c. RNA polymerase binds only to DNA promoters,
which have specific base sequences.

9. RNA Editing
► Many RNA molecules from eukaryotic
genes have sections, called _____, edited
out of them before they become functional.
The remaining pieces, called, _________are
spliced together.
► Introns
► Exons

10. RNA Editing
Is the following sentence true or false?
► RNA editing occurs in the cytoplasm of the
cell.
► False

11. RNA Editing
What are two explanations for why some RNA
molecules are cut and spliced?
► It makes it possible for a single gene to produce
several different forms of RNA.
► It may play a role in evolution, making it possible
for small changes in DNA to have dramatic effects
in gene expression.

12. The Genetic Code
Proteins are made by joining ________into
long chains called polypeptides.
► Amino acids

13. The Genetic Code
► How can only four bases in RNA carry
instructions for 20 different amino acids?
► The genetic code is read three letters at a
time, so that each “word” of the coded
message is three bases long.

14. The Genetic Code
What is a codon?
► It consists of three consecutive nucleotides
that specify a single amino acid that is to be
added to a polypeptide.

15. The Genetic Code
Circle the letter of the number of possible
three-base codons.
• 4
• 12
c. 64
d. 128

16. The Genetic Code
Is the following sentence true or false?
• All amino acids are specified by only one
codon.
► False

17. The Genetic Code
Circle the letter of the codon that serves as
the “start” codon for protein synthesis.
a.UGA
b.UAA
c. UAG
d. AUG

18. Translation
What occurs during the process of
translation?
► The cell uses information from messenger
RNA to produce proteins.

19. Where does translation take place?
► Translation takes place on the ribosomes.

20. Circle the letter of each sentence
that is true about translation.
► Before translation occurs, messenger RNA is
transcribed from DNA in the nucleus.
► It is the job of transfer RNA to bring the proper
amino acid into the ribosome to be attached to the
growing peptide chain.
► When the ribosome reaches a stop codon, it
releases the newly formed polypeptide and the
mRNA molecule.

21. What is an anticodon?
► The three bases on a tRNA molecule that
are complementary to one of the mRNA
codons.

22. The Roles of RNA and DNA
Match the roles with the molecules.
Roles
► Master plan - DNA
► Goes to the ribosomes in the cytoplasm - RNA
► Blueprint – RNA
► Remains in the nucleus - DNA

23. Genes and Proteins
► Many proteins are_____, which catalyze and
regulate chemical reactions.
► Enzymes

24. Is the following sentence true or
false?
Genes are the keys to almost everything that
living cells do.
false

25. Translation Four Major Steps
►A. Messenger RNA is transcribed in
the nucleus then enters the cytoplasm
and attaches to an ribosome.
►B. Transfer RNA translation begins at
AUG, the start codon. Each anti-codon
of tRNA complements a codon of
mRNA and binds a specific amino acid.

26. Translation Four Major Steps cont.
► C. The polypeptide “assembly line” as the
codons bind amino acids the ribosome joins
them together forming long chains of amino
acids.
► D. Completing the Polypeptide the process
continues until one of three stop codons is
reached.